1. Field of the Invention
The present invention relates to a process for producing riboflavin by fermentation, to a method for providing microorganisms having an improved riboflavin-producing capability, and to strains of microorganisms having improved riboflavin-producing ability. Riboflavin is a isoalloxazine derivative which is used as a vitamin, a medicament for beriberi, a feed additive for livestock and poultry, and a colorant for food.
2. Discussion of the Background
Riboflavin has previously been produced by fermentation processes in which Eremotheium ashbyii, Ashbya gossypii, Candida flalerii or Bacillus subtilis is cultured in a carbohydrate-containing medium and riboflavin accumulates in the culture medium (Progress in Industrial Microbiology, Vol. 1, p. 139 (1959); Belgian Patent No. 890,917; and Japanese Patent Publication No. 10,155/78). These microorganisms, however, produce riboflavin only in low concentration or produce it only very slowly. They are, therefore, not satisfactory in a method for commercially producing riboflavin.